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Abstract:

A method of making a motor stator core having a back iron and a plurality
of teeth extending radially inward from the back iron includes providing
the plurality of teeth and the back iron from oriented steel so that a
magnetic flux transmission path is formed with superior properties in
essentially one direction. At least one of the plurality of teeth and the
back iron is annealed in selected portions so as to improve magnetic flux
transmission in a second direction, different from the one direction.

Claims:

1. Method of making a rotating electric machine stator core having a back
iron and a plurality of teeth extending radially inward from the back
iron, the method comprising:providing the motor stator core whose
plurality of teeth and back iron are made from oriented steel so that a
magnetic flux transmission path is formed with superior magnetic
properties in essentially one direction; andannealing at least one of the
plurality of teeth and the back iron in selected portions so as to
improve magnetic flux transmission in a second direction, different from
the one direction.

2. The method as recited in claim 1 wherein providing the motor stator
core comprises providing a plurality of segments, each segment consisting
of a tooth and a portion of the back iron, each tooth being made from
oriented steel so as to have a magnetic flux transmission path in an
essentially lengthwise direction and each portion of the back iron being
made from oriented steel so as to have a magnetic flux transmission path
in an essentially lengthwise direction, and wherein annealing at least
one of the plurality of teeth and the back iron includes annealing a
portion where each of the plurality of teeth is connected to the portion
of the back iron so that the magnetic flux transmission path with
superior properties of each of the teeth is perpendicular to the magnetic
flux transmission path with superior properties of each of the portions
of the back iron.

3. The method as recited in claim 2 wherein the annealing each of the
teeth to each of the portions of the back iron includes welding each of
the teeth to each of the portions of the back iron.

4. The method as recited in claim 1 wherein providing the motor stator
core comprises providing a continuous circular stator and wherein
annealing at least one of the plurality of teeth and the back iron
comprises:annealing a portion of the plurality of teeth so as to remove
the superior properties of the magnetic flux transmission path in the one
direction; andannealing a portion of the back iron at an area
perpendicular to the annealed portions of the plurality of teeth so as to
the remove superior properties of the magnetic flux transmission path in
the one direction.

5. The method as recited in claim 4 further comprising:stacking the
continuous circular stators so that the annealed portions of the teeth
and the back iron are staggered at a predetermined angle from each other.

6. The method as recited in claim 4 wherein annealing the portions of the
plurality of teeth and the portions of the back iron includes applying
energy to the portions by using a rapidly changing magnetic field with
substantially the same direction of magnetic flux that the completed
motor will develop in operation.

7. The method as recited in claim 4 wherein annealing the portions
includes applying heat to the portions at a high temperature followed by
cooling the portions.

8. The method as recited in claim 4 wherein annealing the portions
includes applying heat to those portions while simultaneously cooling the
other portions of the stator where the oriented properties are to remain.

9. Stator core lamination for a rotating electric machine including a
circumferential annular back iron portion and teeth extending radially
inward from the back iron portion, the improvement comprising:said teeth
being radially anisotropic.

10. Stator core lamination for a rotating electric machine including a
circumferential annular back iron portion and teeth extending radially
inward from the back iron portion, the improvement comprising:said
backiron portion characterized by anisotropic regions and isotropic
regions.

11. Method of making a rotating electric machine stator core lamination,
the method comprising:punching a lamination including back-iron and teeth
from oriented steel; andselectively annealing at least one of a tooth and
a selected portion of back iron.

12. Method of claim 11 wherein selectively annealing comprises annealing
selected teeth and portions of back iron having pre-annealed orientation
not substantially aligned with a local magnetic flux to be generated
within the stator core during electric machine operation.

Description:

TECHNICAL FIELD

[0001]This disclosure relates to methods of making motor stator cores.

BACKGROUND

[0002]Motor cores are usually made out of sheets of steel material, which
can be oriented or non-oriented. Oriented steel has oriented, or
anisotropic, properties in the direction that the steel is stretched or
rolled, thereby having superior magnetic properties in that direction of
rolling. On the other hand, oriented steel has inferior properties in the
other, crosswise directions of rolling. Since stator cores of motors are
round and have flux flowing in perpendicular directions in the teeth
(radial direction) and back iron (around the circumference), the use of
oriented steel helps magnetic flux transmission in one area of the
stator, but hurts it just as much in a different area of the stator so
that its overall effect is usually zero. Thus, almost all motors use
non-oriented steel.

[0003]In non-oriented steel, the steel is typically rolled in one
direction and punched using dies into the desired shape. In many cases,
the entire piece is then annealed to remove any incidental directional
properties due to rolling and punching. As a result, the magnetic flux in
motors made of non-oriented steel flow through the steel moderately well
in any direction with no direction of flow being superior to another and
no direction being inferior to another.

[0004]However, it would be desirable to provide a motor stator that
utilizes the benefits of both oriented and non-oriented steel so as to
obtain the more efficient, magnetic flux transmission in some areas of
the stator without sacrificing magnetic flux transmission in a direction
cross-wise to those areas.

SUMMARY

[0005]A method of making a motor stator core having a back iron and a
plurality of teeth extending radially inward from the back iron includes
providing the plurality of teeth and the back iron from oriented steel so
that a magnetic flux transmission path is formed with superior properties
in essentially one direction. At least one of the plurality of teeth and
the back iron is annealed in selected portions so as to improve magnetic
flux transmission in a second direction, different from the one
direction, such as the direction perpendicular to the one direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]One or more embodiments will now be described, by way of example,
with reference to the accompanying drawings, in which:

[0007]FIG. 1 is a cross-sectional view of a tooth and a portion of a back
iron of a segmented stator made in accordance with the present
disclosure;

[0008]FIG. 2 is a cross-sectional view of a stator core made in accordance
with a first embodiment of the method of the present disclosure; and

[0009]FIG. 3 is a cross-sectional view of a stator core made in accordance
with a second embodiment of the method of the present disclosure.

DETAILED DESCRIPTION

[0010]Referring now to the drawings, wherein the showings are for the
purpose of illustrating certain exemplary embodiments only and not for
the purpose of limiting the same, FIG. 1 shows a segmented motor stator
core made in accordance with the method of the present disclosure. A
segmented stator core is typically utilized in small motors because the
wires can be wound very closely around the individual segments before
assembly into a circular stator. First the steel is rolled in a first
direction and the individual teeth 10 and back iron portions 12 are
punched so that the magnetic flux transmission path would be in a
lengthwise direction in both portions as shown by the double ended arrows
of FIG. 1. Then, each of the teeth are coupled to the back iron portions
via welding so that the magnetic flux transmission path of the teeth is
perpendicular to the magnetic flux transmission path of the back iron
with a region of annealed, non-oriented steel 13 (e.g. weld) between
them. Once the individual segments are assembled, the stator core 14 will
have the magnetic flux transmission paths with superior properties in the
directions as shown in FIG. 2.

[0011]Turning now to FIG. 3, there is shown a motor stator core made of a
continuous circular stator comprising a plurality of teeth 10 extending
radially inward from the continuous back iron 12. In this application,
the stator is punched from steel rolled in one direction. This type of
stator is more difficult to improve because the magnetic properties of
the oriented steel are in one direction all of the way around each
lamination. In one embodiment, a portion of the teeth 10 are annealed to
remove the directional properties, such as at the 12 o'clock and 6
o'clock positions. Portions of the back iron 12 are annealed at areas
perpendicular to the annealed teeth 10, such as at the 3 o'clock and 9
o'clock positions. Another portion of the teeth 10 are not annealed, such
as at the 3 o'clock and 9 o'clock positions. Other portions of the back
iron are not annealed, such as the 12 o'clock and 6 o'clock positions.
The teeth and back iron in the positions not already described would then
receive some intermediate degree of annealing.

[0012]This annealing of the teeth and back iron in selected portions will
improve magnetic flux transmission in the core of the completed motor in
the annealed portions because, prior to annealing, the superior direction
for magnetic flux in the pre-annealed oriented material is not
substantially aligned in all places around the stator with the magnetic
flux that will be developed in normal operation.

[0013]For the embodiment shown in FIG. 3, the stator core can be stacked
in a staggered pattern, wherein the annealed portions would be at a
predetermined angle between each lamination or group thereof in the
stack, such as 120 degrees. In this case, each feature of the stacked
stator core, such as a given tooth 10, would be composed partly of core
material with the orientation at or near the most helpful direction and
partly of material having been annealed and therefore having no
orientation. Thus, according to this embodiment of the disclosure, the
magnetic properties of the completed stator core would be improved over a
stator core composed entirely of non-oriented material.

[0014]The annealing of the continuous stator can be by applying energy to
the selective portions. In a first method, energy, such as heat, can be
applied suddenly to selective portions of the stator to heat it
significantly above the threshold temperature for annealing, so that
annealing takes place relatively quickly, and then cooling the selective
portions before the temperature of the remainder of the stator has
increased to the annealing temperature. Alternatively, the energy can be
applied to the selective portions while simultaneously cooling the
non-selective portions so as to establish an essentially steady-state
temperature gradient in the stator for the annealing process, so that
some of the stator is above annealing temperature and some of the stator
is below the annealing temperature.

[0015]Thus, by selectively annealing portions of the stator core where
directional properties work against the overall performance of the motor,
such as in the back iron, while leaving the directional properties intact
where they aid the overall performance of the motor, such as the teeth,
the core losses are decreased while the efficiency is improved.

[0016]Core losses can be used to apply energy selectively to the stator
core. Applying a strong, fluctuating or alternating magnetic field to the
stator core with a similar pattern of magnetic flux as the motor would
develop in normal operation will cause greater losses, and therefore
greater heat to be applied, in portions of the stator core where
directional properties of the oriented steel would work against the
overall performance of the motor in normal operation. That is, a rapidly
varying magnetic flux traveling around the back iron, which the stator
will develop in normal operation, will cause the greatest heating
wherever in the back iron that the superior direction for the
transmission of magnetic flux is crosswise to the flux. This heat
gradient is beneficially utilized to selectively anneal those portions
where heating is greatest (i.e. portions where flux transmission is least
efficient).